Fixed Assets - Summary of Fixed Assets (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Property, Plant and Equipment [Line Items]
Cost	$ 865.6	$ 752.3
Accumulated Depreciation and Amortization	(485.3)	(402.0)
Net	380.3	350.3
Furniture and office equipment [Member]
Property, Plant and Equipment [Line Items]
Cost	238.8	211.9
Accumulated Depreciation and Amortization	(162.5)	(138.0)
Net	$ 76.3	$ 73.9
Furniture and office equipment [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Useful Life (in years)	3 years	3 years
Furniture and office equipment [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Useful Life (in years)	10 years	10 years
Leasehold improvements [Member]
Property, Plant and Equipment [Line Items]
Cost	$ 66.5	$ 66.9
Accumulated Depreciation and Amortization	(32.3)	(27.6)
Net	34.2	39.3
Purchased software [Member]
Property, Plant and Equipment [Line Items]
Cost	122.8	108.4
Accumulated Depreciation and Amortization	(90.9)	(83.0)
Net	$ 31.9	$ 25.4
Useful Life (in years)	3 years	3 years
Software development costs [Member]
Property, Plant and Equipment [Line Items]
Cost	$ 404.7	$ 332.6
Accumulated Depreciation and Amortization	(169.8)	(124.9)
Net	$ 234.9	$ 207.7
Software development costs [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Useful Life (in years)	3 years	3 years
Software development costs [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Useful Life (in years)	7 years	7 years
Leased equipment [Member]
Property, Plant and Equipment [Line Items]
Cost	$ 32.8	$ 32.5
Accumulated Depreciation and Amortization	(29.8)	(28.5)
Net	$ 3.0	$ 4.0
Leased equipment [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Useful Life (in years)	3 years	3 years
Leased equipment [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Useful Life (in years)	4 years	4 years